This invention relates generally to sensing devices and more particularly to a land vehicle sensing device.
Prior art sensing devices have been devised to detect the intrusion of objects into a specified area. These devices have required direct contact with such objects or have set up an acoustic or electromagnetic wave pattern which is subject to disturbance or distortion by the intruding objects. These devices, however, have provided but a small sensing radius, have presented logistics problems, and are complex or otherwise somewhat undesirable.
Present day sensing devices have been devised which have reduced the hereinbefore mentioned undesirable features of the prior art sensing devices by utilizing a geophone or other seismic apparatus which sense vibrations of the ground or other point of reference caused by the intrusion of the objects. The output from the geophone is a low frequency electrical signal whose varying voltage is an electrical analog of the ground vibration. The output electrical signal may be utilized to frequency modulate an audio output to produce an audible signal whose frequency variations are proportional to ground vibration or may be utilized to trigger an alarm device or the like. These present day sensing devices have been somewhat unsatisfactory in that they have been unable to discern automatically between the sources of various sensed signals. More particularly, wind, small animals or the like have triggered the alarm device or the like to give a false indication of object intrusion. Furthermore, the present day sensing systems have been unable to reliably distinguish between the presence of various objects such as the presence of personnel and land vehicles.